1. Field of the Invention
The present invention relates to a data output apparatus for data writing on, and reading from, storage memories, particularly storage memories using storage media like an optical disk.
2. Description of the Prior Art
Heretofore, when such data as video-audio data was to be written on or read from a storage device, the data as requested was sent to or transferred from the storage memories in small segments of a specific size for transfer, 64 kilobytes, for example—the size specified by OS.
If a writing request for data was made when another data was being read out from the storage device, the reading would change to the writing and the writing to the reading by turns per data size of the data divided into small segments. Therefore, it may causes that the head of the storage device moves to a specific portion—that is called “seek”—whenever the mode changes.
The storage device generally comprises a hard disc drive including a hard disc as a storage media. Even if out and on such storage device moving picture data with high-bit rate such as MPEG2 are read and written simultaneously, the duration required to seek (in case of a low performance disk, not longer than 20 m.s.) is shorter as comparing with the duration required to transfer the specific size of data (for example, to transfer a specific size of 256 kilobytes at not more than 40 m.s.). Furthermore, the transfer capacity of the storage device was large fully enough for the bit rate of data. Accordingly there are no problems with that system, and it was not necessary to take into consideration the duration required to seek.
However, that was not the case with the storage memories using an optical disk like DVD as storage medium. Unlike when a hard disk drive was used, the duration required to seek was very long (at about one second) as comparing with the duration required to transfer data. Furthermore, the capability of the storage device using an optical disk is very low in transfer (for example, at 10.08 Mbps., the duration needed to transfer a specific size of 64 kilobyte is 50 m.s.) Therefore, if a request for writing is made when a high bit rate moving picture data such as MPEG 2 is being read out, the total bit rate of the data to read out and the data to write could go up beyond the transfer capacity of the storage device. And since the storage device has to seek each time of switching to reading out and writing, and even if the total bit rate of the data to read out and the data to write is close to the transfer capacity of the storage device, those data could not be transferred real-time on account of the “seek” duration needed. The result was that a stream of data like video-audio data would be interrupted in writing or reading data.